1. Field of the Invention
The present invention relates to a transmission of radio packet data and, more particularly, to an apparatus and a method for radio packet data transmission.
2. Background of the Related Art
A radio packet data transmission system is a system that transmits packet data by assigning a channel or time slot to respective subscriber terminals, which are connected to the system. In addition, a plurality of subscribers are able to communicate at high speed using a limited number of channels. A radio communication system using a frequency source should provide fast communication service to many subscribers using limited frequency channels.
A radio communication system may use either a circuit method or a packet method for communicating information. The circuit method is a method of assigning a channel to a respective subscriber. Therefore, if there are many subscribers, a plurality of channels should be secured. That is, a plurality of subscribers are not able to be accepted at the same time, because of the limited frequency source. If a subscriber spends more time on pause or on waiting than that spent on data transmission, while occupying a channel, the utility of the channel is lowered.
The packet method is a method by which a plurality of subscribers can communicate at the same time using a channel, whereby the utility of the radio channel source can be highly increased. And this method may be adopted as a standard method of the Third Generation Partnership Project (3GPP), that is, radio communication of the next generation.
A background art method for radio packet data transmission will be described with reference to the drawings. FIG. 1 is a block diagram of a general cell in a mobile communication system. The cell is an area in which communication service is provided by a base station of a mobile communication system. The cell includes a plurality of terminals 10 and a base station 20.
FIG. 2 is a conceptional view showing a background art method for packet data transmission suggested by the 3GPP. A terminal 10 should connect to the base station 20 and then should be assigned a channel from the base station in order to communicate with other terminals or with a general wired subscriber. In addition, the terminal transmits the packet data through the assigned channel. The process will be described in more detail as follows.
The terminal 10 transmits an access preamble to the base station 20 with a certain electric power on a position P0. If the base station can not receive the access preamble transmitted by the terminal 10 on the position P0, the base station 20 does not generate an Access Preamble-Acquisition Indicator Channel-acknowledge (AP-AICH) response signal.
In addition, after a certain time τp-p has passed, the terminal 10 transmits the access preamble again but on the position P1. The access preamble, which is transmitted from the position P1, is transmitted with a certain increased electric power over that of the access preamble transmitted from the position P0.
The timing interval τp-p between transmitting the access preamble at the P0 and P1 respective power levels is calculated as follows.Minimum τp-p=15,360 chips+5,120 chips*constant(Tcpch)Maximum τp-p=5,120 chips*12=61,440 chips
The time unit of the chip is decided by a bandwidth of spread frequency. The constant Tcpch is a timing parameter decided in an upper layer of the corresponding protocol.
The access preamble transmitted with the power associated with position P1 is transmitted with increased electric power over that of the access preamble transmitted from the position P0. When the base station 20 receives the access preamble, it transmits a response signal AP-AICH to the terminal 10.
The response signal AP-AICH is transmitted within a period of time τp-a1, from the time the access preamble of position P1 is transmitted, and costs 7,680 chips of time or 12,800 chips of time. In addition, the time is decided by the constant Tcpch.
After the terminal 10 receives the AP-AICH signal from the base station 20, the terminal 10 transmits a Collision Detection (CD) preamble using a power setting on a position associated with P2. The CD preamble is transmitted to the base station 20 within a time period τp-cdp from the beginning of the access preamble that is transmitted at the power level associated with position P1. The CD preamble is for preventing a crash, which may be generated when a plurality of terminals request an assignment for the same channel at the same time. In addition, the τp-cdp time is decided by the constant Tcpch, corresponds to 3 or 4 access slots, and costs at least 7,680 chips of time.
After the base station 20 receives the CD preamble, it begins transmitting a Collision Detection-Acquisition Indication Channel Acknowledge (CD-AICH) response signal within a period of time τcdp-a2 since the transmission of the CD preamble began. The period τcdp-a2 is also decided by the constant Tcpch and is 7,680 chips or 12,800 chips.
The terminal 10 that receives the CD-AICH signal begins transmitting a packet preamble, which is an electric power controlling signal, to the base station within a period of time τcdp-pcp since the CD preamble transmission began. The base station 20 controls a Transmit Power Control (TPC) of a Dedicated Physical Control Channel (Down Link) (DPCCH(DL)) using a closed loop power control method for about 10 ms. The τcdp-pcp time is decided by the constant Tcpch and corresponds to 3 or 4 access slots.
The base station 20 that receives the packet preamble periodically transmits an electric power controlling signal, a pilot, and a CPCH controlling signal through the DPCCH of the down link to the terminal 10. The terminal 10 that receives the signals performs an electric level controlling process for about 10 ms. In addition, the terminal 10 transmits a data unit signal, a Cyclic Redundancy Check (CRC) unit signal, and a postamble unit signal through a Physical Common Packet Channel (Up Link) (PCPCH) to the base station 20.
On the other hand, the base station 20 controls a transmission electric power by transmitting electric power signals to the terminal 10 periodically, while the terminal 10 transmits the data.
The time spent on pre-processing the packet data transmission according to the method suggested by the 3GPP is calculated as follows.
 T minimum=τp-p+τp-cdp+τcdp-pcp+packet preamble transmission time  (10 ms)
According to experimental results calculated in accordance with the above-listed equation, the packet data transmission method suggested by the 3GPP needs at least 22.5 ms of pre-processing time. Also, after the pre-processing data is transmitted, an error in the transmitted data can only be identified after the data transmission is finished. Therefore, if there is an error, the whole process should be performed again.
Also, a Common Packet Channel (CPCH) method of 3GPP, which is decided by the ESTI, ARIB/TTC, TI, and TTA in order to set detailed standards for the background art third generation GMS network, the W-CDMA connecting technique, and for the terminal, has problems that data crashes are increased if there are many subscribers who are assigned a certain channel. Additionally, the data transmission process is complex and it is difficult to transmit the data at high speed because overhead data, which control the respective packets, are large.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.